This research proposal addresses three unresolved issues: first, the experiments will characterize more fully the nature and participation of right atrial stretch in the control of vasopressin neurosecretory neuron activity and plasma levels of the hormone; secondly, it will define the interactions of left and right atrial stretch in the control of these neurosecretory neurons and plasma vasopressin concentrations; thirdly, the interactions of combined stretch of the two atria with carotid baroreceptors and cerebral osmoreceptors will be evaluated as to their effects on this neuroendocrine system. Experiments will be carried out on pentobarbital anesthetized cats. These will have standard cardiovascular monitors. Single hypothalamic neurosecretory neurons will be identified antidromically and changes in their activity will be studied during the above manipulations. Attempts will be made to obtain data which indicates the long term effects of these cardiovascular receptors on neuron activity. Plasma vasopressin will be measured by radioimmune assay in samples obtained from animals which are treated experimentally the same as those used for the neuronal activity studies. Comparisons between the neuron activity and hormone data will be made. The data may either provide support for existing hypotheses regarding vasopressin control or suggest the need for modifying these hypotheses.